Automobile bodies and many industrial and consumer articles are conventionally spray painted in areas called spray booths, wherein water curtains are employed to cleanse the air of over-sprayed paint. The wash water is then treated to remove paint solids, and the treated water is recirculated.
A water curtain is typically created by pumping water into a trough above the over spray area. The overflow from the trough is controlled so that a uniform sheet of water falls along the length of the trough and down the booth's wall. Spray nozzles are also commonly used. Fine droplets of over-sprayed paint, emitted by a spray gun, contact and are captured by the water curtain. The amount of paint contacting a water curtain may change depending on a number of variables, including plant or process shutdowns, the size and shape of the object being painted, the type of spray equipment used, the spraying and purge technique used, and the water flow and type of paint used.
A major problem associated with spraying operations concerns the tacky or adhesive nature of the over-sprayed coating materials. Solids tend to agglomerate and accumulate on the walls, ceiling and floor of the spray area and to clog water spray equipment, recirculating pumps and the like. Paint that sticks to spray booth surfaces usually cannot be easily removed from the equipment and tends to build up over time, which hampers spray booth efficiency. Thus, the over-spray, or paint mist, captured in the water system of a spray booth must be detackified, or "killed", before it adheres to the walls, piping, etc., of the spray booth.
The term "paint killing", as used herein, refers to the act of detackifying over-sprayed paint in paint spray booths.
The term "solvent-based paints" as used herein refers to all common varieties of water insoluble coatings commonly applied in spraying operations, including but not limited to oil base paints, enamels and lacquers. As used herein, the terms "solvent-based paints" and "water-based paints" are synonymous.
A wide variety of chemicals have been proposed as treating agents for circulating wet spray booth waters containing over-sprayed paint, including compositions containing polymers and amphoteric metal salts which form insoluble hydroxides at pH's greater than about 7. The use of combinations of this type are described in the following U.S. Patents: U.S. Pat. Nos. 3,861,887 to Forney; 3,990,986 to Gabel et al.; 4,002,490 to Michalski et al.; 4,130,674 to Roberts et al.; and 4,440,647 to Puchalski. Further, U.S. Pat. No. 4,637,824 to Pominville discloses the use of silicates and polydiallyldialkylammonium halides with amphoteric metal salts, and U.S. Pat. No. 4,853,132 to Merrell et al. discloses the use of precipitates formed by the reaction of cationic polymers and salts of inorganic anions to detackify solvent-based paints. Bentonite clays, aluminum salts and zinc salts have also been used with cationic polymers.
U.S. Pat. No. 4,656,059 to Mizuno et al. relates to the use of melamine-aldehyde acid colloid solutions for treating paint in wet spray booths, and U.S. Pat. No. 4,629,572 to Leitz et al. relates to the use of urea or amino triazine-aldehyde condensation reaction products in combination with water-swellable clays to treat paint spray booth wastes.
While these compositions are generally effective in detackifying and removing paint over-spray, problems of varying degree still remain with paint tackiness, "live" paint remaining after treatment, and incomplete water clarification.
The instant invention represents an alternative to the inventions of the prior art in that a stable, water-based alkaline composition containing a mixture of poly(N-methylolacrylamide) and poly(diallylamine), used in conjunction with a flocculant, can be used with great efficiency to treat circulating paint spray booth waters containing all types of paints and particularly solvent-based paints, lacquers and enamels.